1. Field of the Invention
This invention relates to shaft seals and in particular to elastomeric molded lip shaft seals having a polytetrafluoroethylene wear surface.
2. Description of the Prior Art
Polytetrafluoroethylene seals are presently being manufactured for severe sealing applications, however, these polytetrafluoroethylene seals require new mold tooling in order to be manufactured. Some of the advantages of the polytetrafluoroethylene seal are obtained by applying a polytetrafluoroethylene coating to molded elastomeric seals. For example, it is also known to form a molded elastomeric shaft seal and then to coat the sealing element with a thin layer of polytetrafluoroethylene as by spraying or dipping (see U.S. Pat. No. 2,932,535). A process for allegedly forming a multiple material seal having an inside made of a less expensive material and a liner of Viton or allegedly Teflon is described in U.S. Pat. No. 3,493,645. It is also known to form an annular shaft seal of the type having a trimmed lip by using a standard mold and placing a polytetrafluoroethylene ring in the mold with a pre-form of elastomer on top of the ring, such that when the mold closes the elastomeric material forms the polytetrafluoroethylene ring into a liner. After the molded seal is removed from the mold cavity it is trimmed at a critical location to produce a trimmed lip at a predetermined point; the polytetrafluoroethylene liner will therefore exist bonded to the molded elastomer from the contact point of the sealing lip axially outwardly in one direction only away from the lip. A method for making shaft seals having a trimmed lip (but without a polytetrafluoroethylene liner) is shown generally in U.S. Pat. No. 3,276,115 wherein the trimming is done along line X--X in FIG. 6 thereof.
It is an object of the present invention to provide an elastomeric shaft seal of the molded lip type and a method for making such seals using only the same tooling used in making common molded lip elastomeric seals.